Novel mechanism of stream formation in coastal wetlands by crab–fish–groundwater interaction

A novel mechanism of stream development in coastal wetlands was observed in the form of interaction between the burrowing crab (Chasmagnathus granulata) and groundwater seepage. This process may eventually be further promoted by the predatory action of the white croaker fish (Micropogon opercularis). These so-called crab streams occur on the banks of major tidal channels in a salt marsh of the Bahía Blanca Estuary (Argentina). As the tide recedes, water is retained in the crab burrows on the marsh surface. The presence of lateral burrows produced by crab recruits promotes subterranean piping flow driven by the hydraulic head in the vertical burrow. Groundwater generally seeps along the tidal channel banks but is particularly prominent and concentrated where crab burrows perforate the banks. Where predatory attacks by the croaker fish enlarge the burrow mouths, the drainage rills become wider and deeper because more seeping water is collected in the shallow crater from where it is funnelled into the developing streams. The crab stream is then produced by water draining from the crab burrow mouth, acting initially by cut-back erosion and followed by forward erosion of the relatively unconsolidated muddy sediments.     

Evaluation of the Effect of Penetration Ratios on Composite Grounds Improved with Sand Compaction Piles

In this paper, centrifuge model tests were conducted in order to understand the deformation characteristics and behavior of sand compaction piles (SCPs) reinforced grounds in relation to area replacement ratios and penetration ratios. To simulate ground stress conditions, preliminary compaction was conducted to form grounds that maintained a certain level of strength. SCPs were installed in the grounds using compaction methods, and the relationship between loads and settlement as well as stress under rigid loading conditions were compared and analyzed. In addition, finite element analyses were conducted in order to verify the results of the centrifuge model tests and assess the effects of penetration ratios and depths on variations in stress. According to the results of the analyses, stress concentration ratios gradually decreased as depths increased, and the decreasing rate increased as penetration ratios decreased. However, in regions close to the surface layer in depth in which SCPs were installed, stress concentration ratios showed almost the same range regardless of penetration ratios. Stress concentration ratios showed proportional relations with penetration ratios. However, they showed similar values in regions close in depth to the surface of the ground. In particular, they showed very close ranges at penetration ratios of 100% and 80%.     

海阳市典型砂质海岸侵蚀机制与防护对策研究

海阳市砂质海岸资源丰富,延绵近120 km,尤以万米沙滩浴场著称,但近年岸滩侵蚀严重影响其社会经济发展.本研究基于海阳市羊角畔两侧长约20 km典型砂质海岸连续3 a的海岸线蚀和典型剖面蚀淤调查,定量化研究海滩侵蚀及其变化,辅以一维数值模型,研究人类活动影响下的泥沙运动特征和海滩侵蚀机制.研究结果表明,调查区42.5％...     

蟹类底栖动物对河口潮滩无机氮界面交换的影响

以长江河口的沿岸及岛屿潮滩高潮滩湿地为研究区域,结合现场调查和实验室模拟分析,初步研究了大型穴居底栖动物无齿相手蟹(Sesarma denaan)活动对长江口潮滩沉积物-水界面无机氮交换以及界面处氮的生物地球化学循环的影响。结果表明,高潮滩蟹类底栖动物活动对潮滩滩面地貌施加了显著的改造作用,蟹类活动较集中的地段,蟹洞覆盖率达到2%~3%,滩面掘出沉积物高达1~1.5 kg/m2。潮水淹没情况下,小范围内高密度的蟹类活动能通过机体排泄、加强沉积物再悬浮及促进沉积物-水界面溶质交换等方式致使沉积物出现三态无机氮的巨大释放。蟹类活动造成的洞穴结构及对沉积物的翻动混合能增加沉积物中的氧气含量,促进沉积物中有机氮的矿化和NH4 的释放,造成无机氮在沉积物中的剖面分布特征发生较大变化。     

不同底质粒径下双齿围沙蚕潜底能力和分布特征的研究

Perinereis aibuhitensis(Grube, 1878) lives in marine sediments of estuary or shoal areas, where substrate has some crucial environmental factors affecting its burrowing and distribution. In order to provide basic data for the habitat selection and suitability evaluations of the artificial aquaculture of P. aibuhitensis, this paper conducted a quantified analysis of its burrowing ability and explored its behavioral preferences in different substrates,including mud(75 μm), fine sand(125–250 μm), medium sand(250–500 μm), coarse sand(500–2 000 μm), gravel(2 000–4 000 μm) and ceramsite(4 000–8 000 μm). The research results revealed that substrate grain size significantly affected the burrowing time, burrowing rate, burrowing depth and distribution rate(P0.01).Moreover, P. aibuhitensis demonstrated preferential selections relating to substrate grain sizes, had higher burrowing ability in ceramsite, mud and fine sand compared with other substrates. The strongest burrowing ability and the highest distribution rate were observed in ceramsite. The study indicated that P. aibuhitensis was sensitive to substrate grain size, which also had an impact on its burrowing process and population distribution.In the natural sea, substrates mainly composed of mud and fine sand are fit for aquaculture and stock enhancement. Based on behavioral preferences and ecological rehabilitation function of P. aibuhitensis, this paper proposes a symbiotic system of marine animals and halophytes, and constructs an ecosystem model of"Marine fish-Halophytes-Perinereis aibuhitensis" with P. aibuhitensis as the link.     

粉砂淤泥质海岸人造沙滩效果——以上海金山城市沙滩为例

上海市金山区位于杭州湾北岸,发育典型的粉砂淤泥质海岸,潮滩低平、颗粒极细,下陷0.1~0.2 m,且风暴潮期间海水泥沙含量极高,泥层易滑塌。2005年,在金山潮滩构筑3.3 km封闭式围堰围海成湖1.72 km2,近岸抛沙15.6万m3并设防泥网建成长度1.4 km的人造沙滩进行跳相养滩,后经多次补沙和围堰加固,将“黄水黑滩”变为“碧海金沙”,成为金山城市沙滩。该人造沙滩是中国首个泥岸养滩成功案例,后有天津东疆浴场、潍坊央子人造沙滩、南通启东碧海银滩等10余个人造沙滩建成。金山城市沙滩封闭式围堰消浪护沙、稳定沙滩,结合“沉泥碧水”技术维持海水清洁且防止新滩泥化;固定式防泥网较为坚固,保证游人安全。其围海成湖、沉泥碧水、抛沙建滩及泥沙界网等工程技术为中国粉砂淤泥质海岸人造沙滩建设提供了实践经验。     

泥岸养滩技术与效益评估——以天津东疆浴场建设和评估为例

天津塘沽东疆港区海岸位于海河口和永定新河口之间,是典型的粉砂淤泥质海岸,潮滩低平,沉积物黏、滑而下陷,海水含沙量极高,风暴潮期间水深浪大,缺乏建沙滩的工程地质条件。通过采取建3.8 km长的半封闭防波堤围堰、竹筏—土工布沙泥隔板、双沙泥界网和人工抛沙20万m3等措施,于2008年建成长1 370 m,宽140 m的人造沙滩。泥岸养滩是我国的首创,国外尚无一例。目前我国在淤泥质岸上已建了十多个人造沙滩,最成功的有上海金山、天津东疆和潍坊央子3处,分别在建围堰、隔板、界网以及沉泥碧水等方面积累了较好的经验。     

Reply to J.J. Muñoz-Perez et al. Comments on “Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SW Spain” by E. Poizot et al. (2013) Geo-Marine Letters 33(4)

In a novel finding for a beach environment, Poizot et al. (2013) identified an FB+ trend (sediments becoming finer, better sorted and more positively skewed upshore) on a well-developed swash bar on the upper foreshore of the Camposoto beach of Cádiz in SW Spain. In their Discussion of that paper, Muñoz-Perez et al. (2014) provide some supporting arguments and also report grain-size, beach profile and other data from nearby beaches which differ from those of Poizot and colleagues for Camposoto beach, pointing out that a trend observed on one beach may not apply to a neighbouring beach. However, even though the absolute values differ, the overall trends actually do show the same general behaviour. In our Reply to their comments, we also address some difficulties in comparing granulometric datasets generated by different analytical techniques.     

长江河口岸滩侵蚀演变模式

长江河口地区由于流域带来的泥沙沉降堆积,形成了巨大的长江三角洲平原和水下三角洲。近年来,由于水土保持和流域建水库使得入海泥沙迅速减少,造成长江河口区岸滩侵蚀态势逐渐加重。根据多年海图资料得到的岸滩剖面变化,长江河口区岸滩侵蚀的演变模式按岸滩侵蚀剖面形态特征分为平直型、宽陡型和尖陡型;按剖面的变化特征可分为平行后退型、下凹变上凸型和宽陡变尖陡型。     

淤泥质海床相邻的岬湾沙滩剖面特征研究

通过对浙江沿海岬角海湾沙滩多处典型剖面的调查,结果表明沙滩与淤泥质海床存在较明显的沙泥分界线,滩面物质自北至南,粒径差别不大,中值粒径在0.15~0.25mm之间,滩面基本呈现单一坡度,坡度为1∶15~1∶30,沙滩坡度与波浪动力相关,沙滩前沿波浪动力强,滩面较缓,反之滩面较陡。沙滩退化表现为滩面的截断、粗化和泥化,滩面截断导致沙滩面积减少,中、细沙供给不足;细沙采挖或局部工程导致的沿岸输沙动力条件的改变会使滩面物质变粗;岬湾的水动力条件减弱,易使沙泥分界线抬升,局部泥化;过度挖沙会导致沙滩消失成为泥滩。     

Artificial neural network modeling of cross-shore profile on sand beaches: The coast of the province of Valencia (Spain)

The paper describes the training, validation, testing, and application of models of artificial neural networks (ANN) for computing the cross-shore beach profile of the sand beaches of the province of Valencia (Spain). Sixty ANN models were generated by modifying both the input variables as the number of neurons in the hidden layer. The input variables consist of wave data and sedimentological data. To select and evaluate the performance of the optimal model, the following parameters were used: R², absolute error, mean absolute percentage error, and percentage relative error. Finally, the results are compared with the numerical model proposed by Aragonés et al. (2016b Aragonés, L., Y. Villacampa, F. J. Navarro-González, and I. López. 2016b. Numerical modelling of the equilibrium profile in Valencia (Spain). Ocean Engineering, 123:164–73. doi:10.1016/j.oceaneng.2016.07.036[Crossref], [Web of Science ®] , [Google Scholar]) for the equilibrium profile in the study area. The results show a mean absolute error of 0.21?m compared to 0.33?m Aragones’ model, significantly improving the results of the numerical model in the bar area around de Valencia Port. In addition, when comparing the results with other methods currently used (Dean’s or Vellinga formulation), the errors of these compared to ANN are of the order of 167 and 1538% higher, respectively.     

3-D fluid-mud dynamics in the Jiaojiang Estuary, China

A 3-D model has been developed for the muddy Jiaojiang Estuary and adjoining coastal waters, and verified against field observations. To simulate fluid-mud formation, the model uses a fine resolution grid near the bottom and involves coupling processes between hydrodynamics and fluid mud such as the sediment-induced buoyancy, increasing turbulent kinetic energy sink and kinematic viscosity, mixing by internal waves riding on the lutocline, and non-Newtonian properties of fluid mud. The effective hydrodynamic drag was reduced in the presence of fluid mud. It is shown that the estuary is infilled by tidal pumping and that longitudinal and transversal gradients of suspended sediment concentration, salinity, and currents control the formation of mud banks. Thus a 3-D model is necessary to estimate the fate of mud, although the model results are very sensitive to details of the parameterization of the hydrodynamics-mud feedback processes.     

Closure to “anisotropic hydraulic conductivity and critical hydraulic gradient of a crushed sandstone–mudstone particle mixture”

A closure is presented to the discussion of Anisotropic hydraulic conductivity and critical hydraulic gradient of a crushed sandstone–mudstone particle mixture by Salahou, Jiao, and Yousif (2017 Fener, M., and N. Yesiller. 2013. Vertical pore structure profile of a compacted clayey soil. Engineering Geology 166:204–15. doi:10.1016/j.enggeo.2013.08.001.[Crossref], [Web of Science ®] , [Google Scholar]). The relationship between the critical hydraulic gradient and the uniformity coefficient can be limited to two curves. The internal erosion mechanism of soils with different particle grade curves is different. The maximum diameter of fine particles of different particle grade curves can be calculated by a lot of methods. The density of the original paper is the average density. The anisotropic hydraulic conductivity is caused by uneven density distribution. The hydraulic conductivities are tested on the saturated soils. The saturated hydraulic conductivity can be regard as a constant value for a saturated soil.     

Chenier plain development in northern Sierra Leone, West Africa

The coast of northern Sierra Leone, between the Scarcies and Mellacoree estuaries, forms a prograding muddy Holocene plain comprising two separate, as yet undated, clusters of sand cheniers. The general coastal morpho-stratigraphy and available data on regional climatic and sealevel history suggest that alternations between muddy progradation and chenier cluster formation have been controlled by a probable conjunction of several factors, including the local geomorphic framework, a climatically induced change in mud supply, and relative sealevel oscillations since the middle Holocene. The inner chenier cluster was apparently elaborated under conditions of efficient wave action over a deep, largely unfilled Mellacoree estuary and at a time of reduced mud availability. It peters out seaward, probably in response to several factors, including an increase in mud supply from the upland, a negative sealevel pulse resulting in higher rates of mud export from accreted inner tidal flats, increased muddy sedimentation over a shallower nearshore zone, and attenuated wave action as a result of energy capture by accreted estuarine shoals. The outer cluster, which partly fringes the coast, was formed in a mayor embayment representing the terminus of longshore sand drift. It is suggested that its formation may have been favoured by a higher sealevel resulting in efficient winnowing of sands from subtidal muds, a greater propensity for accretion of tidal flats landwards and, consequently, a lower mud supply to the foreshore.

Although the timing of muddy progradation and chenier formation has not been determined, the foregoing interpretation suggests a complex sequence of events, reflecting as much the influence of local morphodynamic factors as external factors.     

南海东北部深水区泥火山的分布与特征

前人在南海东北部发现许多与天然气渗漏相关的规模大小不一的泥火山。受数据类型和分辨率所限,这些泥火山规模大小存在数据断层。利用多波束地形数据,在研究区域新发现了27个直径在300~1 170 m、高度在5~120 m范围内的泥火山,并且这些泥火山大多发育在海底侵蚀作用强烈的峡谷中。南海东北部海底地层中泥质和烃类来源充足,较快的沉积速率构成的超压体系以及强烈的挤压构造应力作用,使得含气高压泥浆上涌,穿透峡谷较薄的沉积层,这些黏性泥质在海底表面堆积形成了泥火山。     

拟穴青蟹大眼幼体和第Ⅰ期仔蟹底质选择的研究

拟穴青蟹大眼幼体和仔蟹对海泥和泥沙底质的选择性显著高于各种粒径的沙底（粒度0.06～2.00mm）.其原因可能与海泥和泥沙底质在流动海水中物理稳定性高于沙砾有关.通过以埋栖选择性和相对埋栖率为指标考察了大眼幼体和仔蟹的栖息方式,发现白昼大眼幼体埋栖在底质中的比例显著高于夜间,也高于仔蟹;夜间大眼幼体栖息方式与仔蟹差别不明显;并发现大眼幼体栖息方式存在着昼夜差异和昼夜节律性.这揭示了拟穴青蟹大眼幼体对底质的选择性和在底质上栖息的方式表现出对FTT机制的适应.     

Characteristics of coastal erosion geometry under regular and irregular waves

An experimental investigation of coastal erosion generated by the action of regular and irregular waves was carried out in laboratory channels. Natural beach sand, with medium diameter of 0.35 mm and specific gravity of 2.63, was used in this study. A 1:5 initial beach slope was selected for the model tests. Different wave groups were generated over the initially flat beach, and the characteristics of coastal erosion geometry such as erosion lengths, erosion depths, location of maximum erosion point, and total erosion areas were measured. The most important parameters governing coastal erosion were evaluated by using earlier investigations and experimental results. These parameters were expressed as a dimensionless group by using π theory. The empirical relationships between the geometric characteristics of coastal erosion and the dimensionless group are proposed through regression analysis for pure regular waves, pure irregular waves, and regular-irregular waves. The parameters, which were used to define geometric characteristics of coastal erosion, were evaluated and some ratios of these parameters gave a constant value.     

珊瑚礁海岸侵蚀的研究方法

珊瑚礁海岸海滩和礁坪是海岸作用是活跃的部分，也是近几十年来与海岸发育，海岸侵蚀联系最密切的部分，这一部分高潮时被淹没，低潮时完全出露或大部分出露，使得在此进行地质填图成为可能，这样的地质图可以提供许多信息，如沉积物粒度分布规律，沉积物来源和搬运方向，海滩岩所指示的古海岸线位置，人类活动特别是海岸工程对沉积物分布的影响以及海岸线的变化过程和趋势，在礁坪上开挖的人工水道内测流，能够了解水流的性质以及是否有足够的速度搬运沉积物，从而了解人工水道对海岸的影响和预测海岸的状态，这些方法也可以用于大陆泥质和砂质第岸侵蚀的研究。     

Subtidal Benthic Macroinfauna in an Estuary of South Chile: Distribution Pattern in Relation to Sediment Types

Abstract. A quantitative survey (18 stations) of the subtidal soft bottom macroinfauna in an estuary of the south Chilean coast was conducted during January, 1980. The map of sedimentological facies elaborated for the Queule River Estuary shows sandy bottoms in the outlet and upper part of the area studied, while the middle part is occupied by muddy sand. The ordination of stations by Principal Component Analysis is fundamentally defined by mud and gravel percentage and is, in general, concordant with the distribution of sediments in the facies map. A total of 17,405 animals was collected (16 taxa), Polychaeta being the dominant group in density (77.47%) and biomass (73.4%). The maximum number of species was obtained outside the mouth of the estuary, while maximum densities and biomass were obtained in the middle of the estuary.
The Factor Analysis performed with the abundances data of the most abundant species rendered the ordination of two groups of stations (concordant with a Cluster Analysis) in the Q-mode and two groups of species in the R-mode. One group of stations is restricted to sandy habitats of the outlet area and is dominated by suspension feeders. The other, in the middle and upper part of the estuary (muddy sand or sandy bottoms with a higher percentage of organic matter), is dominated by deposit feeders. Between these two groups, significant differences in sedimentological variables (sand, mud, and organic matter percentage) were detected. Each of the two delineated groups of species corresponds to the groups of stations, showing that most of the taxa can be combined in faunal assemblages with preference for different types of substrate.     

东沙群岛西南海区泥火山的地球物理特征

多道反射地震和CHIRP浅地层剖面显示在南海东沙群岛西南陆坡和白云凹陷东部陆坡之间的深水(600~1 000m)陆坡上矗立着一系列高出周围海底50~100m的丘形地质体,其内部地层发生褶皱,反射波呈现杂乱和空白,海底声波屏蔽严重。浅地层剖面还显示丘状构造带有气体羽状构造,从海底进入水体高达50m。海底沉积取样分析表明,这些海丘区的表层分布着生物成因的致密碳酸盐结核。可以推断东沙西南的丘形地质体就是泥火山带,并且可能是一个重要的水合物潜在区。东沙西南海区泥火山表现出构造挤压和带状分布的特点,不同于南海北部神狐和九龙甲烷礁已发现水合物区的非泥火山,也不同于全球其他典型被动大陆边缘的泥火山特征,其构造成因和水合物潜力有待进一步研究。